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Do jets breaking the sound barrier leave shredded metal on the ground?
As a kid (1960s and 1970s) we would find shredded metal rolled into a loose ball similar to the shredded paper one might find in an Easter basket, in the hills surrounding our farm. We had the Royal Canadian Air Force (RCAF) based about 60 miles north of us in Moose Jaw, Saskatchewan, and the jets used to fly over the farm quite often. We were told that this metal came from the jets when they broke the sound barrier. I can not find any information to confirm this.

Before any aircraft had flown faster than sound, someone wrote a fictional account of what the first supersonic flight might be like. When the aircraft reached supersonic flight, the nose got smashed in. Then when it slowed down to subsonic flight again, the tail got smashed in. In between, the entropy meters in the cockpit were all running backwards. None of this happens in real life.

Only jets that aren't supposed to break the sound barrier :)

The sound barrier is not made up of metal ;-)

I don't think this had anything to do with military jets breaking the sound barrier nearby; it does sound more like strips of metal recovered from chaff dispensers on the jets; countermeasures systems which eject hundreds of strips or threads made of metal foil used to thwart enemy radars.  Most likely the aircraft discharged their chaff dispensers during training exercises over the farm; you simply recovered some of the metal strips.
Wikipedia

Source

my thought exactly. Thin strips of metal or (later) laminated plastic, coiled up from how they're stored.

That's definitely not true, metal shredding off an airplane is the sign of a structural failure, and is a serious problem. It certainly doesn't happen often.
It's unlikely that they would be going supersonic over land, you'd know it if they did as it creates a very loud bang.
As for what that metal was I couldn't tell you, perhaps they came from the airplanes and perhaps they didn't, if you have a picture please do share it. If I had to guess I'd say could be chaff, metal foil dropped from an airplane as a radar countermeasure.

At airshows, jets frequently go supersonic for demonstrations.  Glass nearby at storefronts does not shatter.  On the other hand, glass sometimes does shatter from aircraft activity.  I don't know why it happens sometimes and not other times.

When airplanes go supersonic at airshows it's with previous approval.

When they do that, why does it not typically break any glass?

@RockPaperLizard Because the boom just isn't big enough.  Shape and mass of the aircraft play into this, and any plane that was going to make a big boom wouldn't be allowed to do one.  Further, bear in mind, glass can only shatter from a sonic boom if it's in a particular situation.  Generally, it has to be the weakest point in a sealed container  so that the pressure differential between the inside and the outside of the container is great enough to break the glass.

@RockPaperLizard Though if you want a fuller explanation, going over to Physics.SE and asking there might be some fun :).  They'll have a more detailed explanation.

When I said been known to break windows I did not mean it happens often. As I can't better qualify the statement and it's not important for the answer I'll simply take that part out.

@JayCarr  Thanks Jay and GdD!

The MythBusters proved that it is extremely difficult to break glass with a sonic boom. (Even with a pass at 200' AGL.)

I wouldn't say that a sonic boom over land is that unlikely. Maybe it's different in Europe, but it happens frequently in the U.S. They usually try not to do it over a major city or similar, but we heard them at least a few times a week when I lived near a US Air Force base. Given our similarly vast and similarly sparsely-populated geography, I wouldn't be surprised if Canada more resembles the U.S. than the U.K. in this regard. However, civilian aircraft are banned from supersonic overland flight over the U.S.

@reirab In Europe sonic booms were also common 50 years ago, but supersonic flying was banned in the 1970s, so such training was re-located to northern Canada.

@PeterKampf There's a whole separate question coming out here, but just to say that I'm pretty sure that in the UK (if not the rest of Europe) supersonic flying over land is banned except in very specific circumstances - mostly just typhoons on QRA. You'd certainly never get it at an airshow.

Here is a video that shows several aircraft breaking the speed of sound, including several still images of it.  You'll notice that none of the images show the skin of the aircraft being affected.
Supersonic Flight and Sonic Booms
There are a lot of misunderstandings regarding breaking the sound barrier, including several theories, that still linger from the 40s and 50s, that an aircraft would simply break apart when it hit the sound barrier.  Those rumors, I think, produced ideas like the one you state here.  I mean, if older planes would have broken apart, perhaps newer planes are only barely surviving by simply shedding metal shavings when they break the sound barrier, right?
Well, the problem is that this argument would be based in a false claim.  Planes didn't break apart simply because they "hit the sound barrier".  In reality, the main issue most aircraft faced when they broke the sound barrier was that their control surfaces would start to lose effectiveness because the supersonic speeds caused the air to separate from the wing.
Approaching the speed of sound will cause super sonic airflow over the front of the wing, changing the center of lift in an effect called Mach Tuck.  Further, fully breaking the sound barrier can then cause direct interference with an aircrafts control surfaces if they are not properly designed (Peter Kämpf's excellent answer, linked above, has all the details).  This could cause the plane to tumble which may, in turn, cause it to break apart.
In essence, it wasn't a materials problem, it was a control surface authority problem.  Once that issues was fixed (as it was for the Bell X-1), the fear of an aircraft breaking up when hitting the sound barrier were mitigated.  No material changes were actually required, the X-1 was made out of plane old aircraft grade aluminum alloy.
In fact, it takes some serious speed before materials come into play at all.  Somewhere over Mach 2 is where we have to worry about the skin failing, but even then, it's not from force (which is what would create metal shavings) it's from extreme heat (like when a space craft is re-entering the atmosphere.)  But we have materials that can deal with that now as well, and we have some craft that can safely go six times the speed of sound without any serious damage to the skin.
Anyway, sorry for the long rambling answer.  It just seemed liked there might be some questions behind your question that you might like addressed.  Hopefully I wasn't to presumption ;).

"plane old" … I see what you did there. (Actually, it's probably a typo, but a cool one.)

@JörgWMittag It actually was on purpose, glad someone appreciated it ;)

As you said in the 60's 70's let me relate what I do know. Aircraft countermeasures were in their infancy. As a kid driving first the Avon Sabre or CA-27, to be more correct (sorta like your Canadair Sabre Mk6 but with balls), which would only go sonic very high going down hill or lower going very, very quickly downhill, then the Mirage IIIO/E which were sonic anywhere you liked (with varying degrees of efficiency) we had rudimentary chaff dispensers (by today's standards) which were rarely armed for normal training. The reason being is that the method of discharging the chaff was like a short little shotgun barrel with a shot gun like cartridge propelling the chaff shot fired electrically.
If on a training mission chaff was used before returning to base you would recycle the system to make sure that there was no misfire that was gunna get your ground grew on the apron. For it to be still balled it may have been a pilot coming in lowish and slowish and the ball didn't have time to disperse.
Why low and slow? 60 miles you would be getting near the point of slowing down on approach. The Sabre not so much but the Mirage yep and as Canada had the 104 definitely yes but Moose Jaw was mainly Canadair CT-114 Tutor (definitely NOT sonic capable) if my time there (on exchange) serves me correct.
Ex Aussie flyer.

You may add links and perhaps picture of those chaff cartridges to illustrate your story, and maybe introduce your story by saying the shredded metal must come from chaff. Those small edits may greatly improve your answer.


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Why do (some) aircraft shake at low speeds with flaps, slats extended?
I landed a couple of times as a passenger with the Embraer 190 (I like Embraer very much) on runways with a length below 2 km.
I noticed that the plane started to shake or vibrate quite strongly once reducing its speed prior to landing. The flaps during this time were fully extended. How can one explain these vibrations? I have to note though, that I often sit in the back of the fuselage, where vibrations tend to be more pronounced.

I would say that the shaking started about 2-4 minutes before touchdown. Just from my memory, I didn't measure the time.

It would be helpfull if you find a video showing those vibrations. This kind of phenomena is hard to describe otherwise

thanks for all the answers! Yersterday I landed again as a passenger with the Embraer 190 on a runway with a length of 2500 meters and didn't notice these vibrations. I posted the question after landing on London City Airport, whose runway length is 1500 meters. I agree that load or weight of the aircraft is an important factor. Everything else being equal, a heavy aircraft will have a higher angle of attack. Up to now, based on your questions, I think that the disturbed airflow hitting the horizontal stabilizer is the answer. Thanks again. There is a lot to learn here.

I landed again on London City Airport as a passenger with the Embraer 190 and it seems that the steeper flight path is responsible for the shaking. I assume that the steeper flight path leads to higher angle of attack, causing the horizontal stabilizer to be exposed to "dirty air" or turbulences induces by the wings, flaps.

There are many phenomena which can cause vibrations. Without knowing further details like the frequency, starting moment or the weather conditions on landing it is difficult say. Common causes are:
Stall buffet/ self induced turbulence Normally when a plane lands it flies with low velocity and a high lift coefficient, near to stall. The flow detaches much earlier and there is more turbulence behind the main wing. The tailplane has to fly through this turbulent zone and hence you feel the vibrations. Sometimes deploying the spoilers, even if you're not flying at stall speed is enough to create turbulence which will hit the tailplane. T-tail airplanes are less affected because they're further away from the air zone influenced by the main wing.
Atmospheric turbulence Can be created due to thermals (in that case it should be sunny) or wind hitting ground structures. If you have landed a couple of times and always felt the vibration it probably isn't the answer.
Wake turbulence Shouldn't be your case either, separation minima exist to avoid this problem and it would probably feel different every time you land.

@mins Possibly, I hadn't seen the time comment. Perhaps someone who has flown the E190 can provide a better answer.

I doubt stall buffet is the answer here. Approach speed (Vref) is no less than 1.3 times stall speed in the landing configuration, and 2-4 minutes out the speed flown is probably at least Vref+20. Vibration from gear would seem more likely here.

I agree with Jonathan that stall buffet is unlikely, but I suspect the added turbulence from the flaps and the high AoA affecting the horiz stab is probably the key. Especially since he was in the rear

You may also mention wake turbulence. During landing each aircraft folow the exact same final approach route to a given runway

Wake turbulence, mentioned by @ManuH, should not be an issue, at least not in routine operations. Air traffic control separates airplanes based on wake turbulence characteristics so that there should be no effects on following airplanes. It's possible, especially when operating not under ATC control, to be in too close, but you probably won't be feeling shaking: you'll feel more like a rolling motion.

I changed the answer to take the comments into account. @JonathanWalters Could you explain what do you mean with gear?

@mns Sorry, by gear I mean the landing gear. On aircraft such as the E190, the wheels and the whole wheel assembly including the shock struts are referred to as landing gear, or simply gear.

@JonathanWalters Yes, I understood that. My bad, with the question I meant to ask why do you think that the gear produces the vibrations- not every plane starts to shake strongly after deploying the gear.

The answer is quite simple: Altitude. Air near the ground, as a general rule, is more turbulent and unpredictable than air aloft. Buildings create mechanical turbulence and there are pockets of updrafts from surface heating (especially over black asphalt runways).
You may also be feeling mechanical vibration from the gear extending, or maneuvering causing airframe oscillations.
Flaps and slats increase the surface area of the wing, which reduces wing-loading, which reduces wake turbulence. The aircraft creating turbulence for its own tail is likely not the answer, and in extreme situations this is actually referred to as a "deep stall" which is quite dangerous.

There are many reasons why the plane is shaking.

The plane may be experiencing turbulence, wind causing plane to not balance.
The plane may stall because the angle of attack is too great.
The engine may have problems running at slow slow speeds

You should do some editing effort (such as line break). An answer is easier to read when well formatted.

@ManuH: Daniel did format it correctly, but didn't know about adding two spaces (or a blank line or ) to force a line change.

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How do modern commercial aircraft handle dust storms?

I live in West Texas where dust storms are an occasional fact of life. I am interested in how modern jet aircraft handle dust storms such as the one seen in the photo. From a pilot POV I can see that sand is no different than fog with high winds. However, from a mechanical standpoint, this is a high velocity abrasive being shot at the vehicle and through the engines.
How do modern airliners and their crews deal with a large sandstorm?
Would a standard weather briefing warn a pilot of the possibility of a sandstorm?
What would the appropriate action be for a pilot who suddenly finds themselves above a sandstorm in a piston or turbine aircraft?
How would a pilot judge when a dust storm is too dense to enter safely?

There is an interesting presentation on the impact of dust on aircraft here. And the Flight Safety foundation has a good article that breaks down a lot of aspects here and is worth the read.
It's not just the reduced visibility, but the associated high winds that can be a real danger for aircraft operating in a dust storm.

Dust storms pose a significant hazard for aviation. Not only do they
  drastically reduce visibility, they also are associated with very
  strong winds that can seriously affect an aircraft in flight. Engines
  can be damaged by ingesting the dust.

But as per your questions directly

How do modern airliners and her crews deal with a large sandstorm?

They most likely will avoid them as they would any heavy weather activity. The extremely reduced visibility might bring the airport below operational flight minimums, thus making an approach or departure impossible.

Would a standard weather briefing warn a pilot of the possibility of a
  sandstorm?

One main issue with dust storms is how fast they come up, and this can make them harder to predict than a storm that is rolling across a region.

It was a typical early summer evening in southern Arizona, U.S., this
  past July 5. At 1751 local time, the Phoenix Sky Harbor International
  Airport was reporting 10 mi (16 km) visibility with winds of 7 kt. But
  all that changed in a matter of minutes.

As for what to do when you find yourself over or in a dust storm check this article out of a firsthand account.

Yea, the simple answer is avoid them, but of course that's not always possible. With enough forewarning, maintenance crews would do their best to get aircraft in hangars, or evacuate them from the area altogether.
Standard weather briefings include current observations, and forecasts for your planned route and destination. Unless a sand or dust storm had been observed though, there is no guarantee that the briefer would provide any sort of warning for it. Here's more on the content of standard flight briefings.
Any reasonable pilot would not be judging whether or not the dust storm was too dense. If its recognizable as a dust storm, it should avoided.

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Is the “competent observer” a required crewmember?
This question came up as a followon to another answer.
14 CFR 91.109 reads in part, with added emphasis:

§91.109 Flight instruction; Simulated instrument flight and certain flight tests.
(c) No person may operate a civil aircraft in simulated instrument flight unless—
    (1) The other control seat is occupied by a safety pilot who possesses at least a private pilot certificate with category and class ratings appropriate to the aircraft being flown.
    (2) The safety pilot has adequate vision forward and to each side of the aircraft, or a competent observer in the aircraft adequately supplements the vision of the safety pilot …

Is the “competent observer” a passenger or a required crewmember?

I think the "competent observer" is a required crewmember if the safety pilot does not have adequate vision to supplement the pilot.

Yes, the "competent observer" is a required crewmember in that situation, by definition.
According to 14 CFR 1.1:

Crewmember means a person assigned to perform duty in an aircraft during flight time.

Clearly, a "competent observer" operating as such under §91.109 (c)(2) is a person assigned to perform a duty in an aircraft during flight time; such an observer is therefore a crewmember. The operator is required to operate the aircraft with that observer performing their observation duties, and that person is therefore a required crewmember.
There are no other requirements as to who this person may or may not be other than the qualifying term "competent". The aircraft operator bears the burden of determining the observer's competency. One might argue that a certified pilot would be a competent observer.
An implied question here might be, is this competent observer a required crewmember that is able to log time for the performance of their duties? To this I would say, no, there is no provision in 14 CFR 61 for the logging of flight time for a person designated as an "observer", competent or otherwise.
EDIT to further explain the above paragraph in consideration of discussion in the comments: 14 CFR 61.51 allows pilots to log PIC and SIC time for flight in, among other conditions, "aircraft for which more than one pilot is required under the [...] regulations under which the flight is conducted". The "qualified observer" is indeed required in the situation in question, but need not be a pilot, and—unless otherwise qualified—is not acting as one of the required pilots in an "aircraft for which more than one pilot is required under the [...] regulations under which the flight is conducted". Obviously, if the person fulfilling the duties of a "competent observer" is otherwise also a required pilot, then the pilot may log the flight time as the required pilot.

I can't agree on the logic that a competent observer is a crewmember who cannot log the time. Either the "competent observer" is a (required) crewmember who can log the time, or the "competent observer" is a passenger. The requirement for logging the time is "required crewmenber", and doesn't need to be any further distinguished in the CFRs, which is why you don't find a specific provision for the "safety pilot" to log time in the regs.

@rbp I suppose anyone can log any time they want in a logbook, but I stand by my assertion that there is no provision in 14 CFR 61 for logging of flight time for an observer. §1.1 defines Flight Time as "Pilot time...", for which definition I would argue an observer does not qualify. There is a difference between "crewmember" and "pilot". I don't know where "required crewmember" is the requirement for logging flight time, but I would be interested in seeing it.

If you are a required crew member, then you get to log the time: 14 CFR 61.51(e)(iii) "When the pilot ... acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted" and a similar 'graph for SIC time.

@rbp That's for pilots, not crewmembers. Crewmembers need not be pilots. Required pilots do indeed get to log flight time as you describe. As you see in §1.1, a crewmember is a person, not necessarily a pilot. Even if the observer happens to be a pilot, that role is not required to be filled by a pilot and therefore does not meet the "more than one pilot is required" criteria. See this question for further clarification (or ambiguity!) on the crewmember definition.

No, it does not need to be a crew member.
If the safety pilot has adequate vision forward and to each side, then no one else is required. Only in a case when there is some hinderance or obstacle in the field of view for the safety pilot, and a competent observer's view is not hindered by that obstacle, then they can be used.
A competent observer is only an observer who is competent in observing. Logically, a crew member is always the first and preferred choice than curious or grumpy passengers. I did not find any details on the qualifications of a competent observer in the CFR.


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What is the aerodynamic effect of a panorama (skydeck) near the tail section of a commercial airline?
A company called Windspeed Technologies posted the following concept video of a panorama seating option aboard a commercial plane.
From the limited understanding I have of the phenomena called flow separation, such a structure on the fuselage may induce separation.

The sphere example here is just an approximate representation for the semi-ellipsoid.
The reason I am asking this question, is because the ellipsoid is relatively near the tail section of the plane. It does not seem like a good idea to have a turbulence inducing structure that close to the tail.
How will this addition to the plane fuselage effect the air flow ? Worst case, can it cause navigation problems due to turbulence near the tail section ?

Is no one else concerened that the customers legs will be cut off when this thing rotates? Seriously, there is no space for the legs anywhere. And people bitch about leg room in economy class.

They already put antennas for internet connection in basically the same place.

You're correct that the structure may induce separation under some conditions. However, the effects are unlikely to be significant given the (publicly) available data on the concept. From the available images, the deck is quite small, with a seating capacity of only two.

Image from gizmag.com
Also, it is located at some distance in front of the vertical fin and appears shaped to reduce drag.

Image from technology.org
The company says that it has over come many design hurdles including

... structural modification, structural integrity of the canopy to withstand a bird strike and flight loads, condensation, noise levels, UV protection, aerodynamic drag, potential disruption to the vertical tail's performance, safety, ingress and egress requirements per the FAA requirements.

Though this should be taken with a grain of salt (it from the company after all), there is nothing insurmountable in the engineering sense. For example, the canopies of fighter jets are of similar size in smaller aircraft and they are operated without problems.
AWACS aircraft routinely carry huge antenna on top of their fuselages; they have no problem flying, albeit with reduced performance. For example, the following image shows the E-767, the AWACS version of Boeing 767 operated by the JASDF.

"E-767 Japan AWACS 112010" by Jerry Gunner - AWACS Boeing E-767 of Hiko Keikai KanseitaUploaded by Altair78. Licensed under CC BY 2.0 via Commons.
However, it is another matter if this is going to enter into service. My take would be that this is not going to happen in current time for a number of reasons including:

The cost quoted is pretty high and downtime, too long.
cutting up pressurized fuselage is not a good idea.
The concept is going to take up seats and increase weight for questionable benefits. What are you going to see up there? the same clouds that you are going to see from normal windows anyway.

So, the "cupola" on top of the airplane is more of a teardrop shape than spheroid or ellipsoid. Many of the control surfaces on aircraft use this shape, so the induced/pressure drag caused by it would not be much and since it is smaller than those surfaces, it would have less of that drag. The addition of that surface adds more surfaces area, which creates more, though somewhat negligent, parasite drag. Overall, the airworthiness of the airplane would not be affected much, although a Supplemental Type Certificate (STC) would be needed to add the structure on.

Which control surface is shaped that way?

@JustSid Wings, horizontal and vertical stabilizers, canards, &c The copula just has a different size ratio than those surfaces.

Any kind of change to the aerodynamic envelope does have an effect on airflow over that section.  This would have been analyzed by engineering using competent CFD modelling and wind tunnel testing.  The end result here is that the effect is probably minimal for several reasons:
First, competent shaping of the protrusion should result in minimal disturbance to the airflow in that region.  Second, the blister shape is mounted on the aft dorsal section of the fuselage, where we would already predict the boundary layer airflow to be turbulent, so flow separation is a minimal issue here.  Third, if the shape is sufficiently placed upstream of the control surfaces and the cross sectional area of the affected surface is limited (say, 5-10% of the total surface), the impact on flight control should be minimal and more than acceptable.


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What kind of supervision do new captains get on their first flight?
Is there any special consideration for the first flight as a captain? I mean, the first officer gets promoted to captain, does his/her first flight gets supervised by any special way?
PS: I'm tagging this question as faa-regulation, not so sure if it is correct.. please correct me if I'm wrong

After a new captain is done with schoolhouse training (classroom and simulator) they will fly on-line as a captain and will have a training captain in the right seat.  After some number of flights (for me it was a 4-day pairing) you will be joined by a check airman in the jumpseat and have a line check.
Once you pass the line check if you are a first time captain you are a high minimums captain for your first 100 hours and then a normal captain. During high mins time you are subject to a few restrictions in approaches you can fly. All the flying after the line check is with normal (low time) first officers.

"you will be joined by a check airman in the jumpseat and have a line check" I'm sorry, didn't get that.. could you explain a little bit please?

@mendieta you'll fly at least one leg with a the new captain in the left seat, a training captain in the right seat and a check airmen in the jumpseat (a third seat in the cockpit).  The line check is a specific kind of checking event where the check airman observes a crew during a normal flight and evaluates the pilots.  In this case the evaluation is to release the new captain to the line to fly with normal first officers.  A captain will get a line check once a year.


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How do I interpret these values in NASA's C-MAPSS dataset files?
I was studying a dual-speed, high-bypass ratio turbofan engine dataset which I happened to obtain from NASA's website. This dataset was generated from C-MAPSS simulator where dataset has nominal and fault files. I studied the user guide doc and some other documents related to the same but I failed to understand the difference between these two files (ie. at the value/ parameter level).
I have following questions, if anyone has used/aware of this dataset please help me:

difference between nominal and fault file
There are 27 parameteres used, among these which parameters will affect fan, HPC, HPT, LPC, LPT
what is the threshold value for these parameters or when do we say that the parameter has reached its max value and above which it would lead to fault condition.

Here is the link where I got the dataset:
c3.nasa.gov/dashlink/resources/140/

Can you link to where you obtained the files?

difference between nominal and fault file

It is found inside the .tar.gz file. From the README file contained in the page you linked:

the Simulation_Info.txt contains a summary of the number of flights,
  the fault type that was simulated, if it is nominal or not, and if not
  what flight and time sample the fault was introduced.

There are 27 parameteres used, among these which parameters will affect fan, HPC, HPT, LPC, LPT

I assume you are asking what are those 27 parameters.
From the README file that is found in the page you linked:

what is the threshold value for these parameters or when do we say that the parameter has reached its max value and above which it would lead to fault condition.

A detailed answer is out of scope for this site, it heavily depends on the failure simulated. The documentation of the various tests should have enough details to understand.
Additionally, hard absolute values are definitely of no use here, different engines will have different characteristics: the numbers valid for the engine simulated here will be applicable to basically no real engine.


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Is it economically viable for Emirates to use a 777 for some of these routes?
This question may sound rhetorical or not well posed, but I wonder what the economic viability or sustainability of certain Emirates routes is.
Among its 164 destinations, Emirates is currently serving a whole host of non-major airports (airports which, according to this list, are not among the 30 busiest in the World). Among them are:

Newcastle upon Tyne (NCL)
Prague (PRG)
Bologna (BLQ)
Harare (HRE)

and so forth.
My question: on the majority of these routes, a Boeing 777 is deployed. But how economically viable could it be to fly such a high-capacity plane to destinations where the target market is not so wealthy or not big enough? In some of these instances, Emirates is the sole airline operating the Boeing 777. Also, I speculate that other airlines would probably use another, smaller aircraft to some of these destinations. I am sure Emirates does its market researches with adequate meticulousness before opening any new route, but I am still doubtful - couldn't the people living around Bologna take a train to Milan to get to Dubai, for instance, given their close proximity?

I'm not sure why you describe those places as not wealthy enough. Not being in the world's 30 busiest airports doesn't exactly make you a backwater. And don't forget that flights go both directions. Prague in particular is a big tourist destination.

If you want to know for sure, you will need to spend some money. For free, all I could find is that Emirates had an overall load factor of 80% in their 2011/12 fiscal year, which is slightly above the usual threshold for profitability.

They might be saving money and optimizing schedules by avoiding the busy airports in favor of less busy ones nearby.

That's not nearly the case, my friend.If you check their destination list, you'll figure out there are smaller airports not very far away from bigger ones. The example I made calls for a distance of approx. 250 km from Bologna to Milan Malpensa Airport. Same thing in the UK: in the north, apart from Edinburgh and Glasgow, they serve Newcastle, which is 90 minutes south of the former by train.

@FC84 Who wants to drive or take a train for 250 km when you can just fly out of your own city? Also "not in the busiest 30 airports in the world" doesn't make an airport "non-major." By definition, if you serve 164 destinations, at least 134 of those are not in the top 30 in the world.

A lot of this can also be corporate strategy (sometimes foolhardy). To aggressively grow or gain market share sometimes companies do things that are not sustainable in the long run. When your principal stakeholder is a sovereign entity strange moves can happen. I'm not saying this is entirely true in this case, but its something to keep in mind.

Another important point is the savings in maintenance / spares / purchasing / training costs by standardization across the fleet. Sure, low load factors pinch, but not having to maintain a diverse fleet offsets some of that. Besides you can get some crazy discounts from Airbus & Boeing on large orders.

As far as deploying a 777 versus something smaller, Emirates only has  widebody aircraft -- A380, B777, A340, A330 -- in its fleet http://www.emirates.com/english/flying/our_fleet/our_fleet.aspx

Since you asked, at least PRG -DXB was upgraded to A380. Definitely profitable (they have good connections to Asia and Africa, so they sucked most of the tourist market between those places).

There are many reasons an airline may fly to a given destination and the economics of air travel are complex to say the least. I would like to fist address your question

couldn't the people living around Bologna take a train to Milan to get
  to Dubai

Sure they could but airlines don't only service locations because of the people that live there they may service them for the very people that don't. I fly both commercially and as a GA pilot to explore new places. I generally fly out of the Philadelphia area which is one of the busiest in the US. From there I head to plenty of tiny airstrips all over the place, none of these airstrips are in towns that are as economically prosperous or busy as Philadelphia but they see my travel because I wish to explore the area. The same goes for foreign airports, simply because a country is less economically prosperous or "busy" than another does not mean it has less to offer culturally and in fact may be a hot bed for tourism.
I have personally been to both Prague and Bologna and they are great cities both with large tourist markets. I can see it being very economical to fly a wide body airliner there full of tourists and maybe only a few locals. While layovers may attract the lower budget fliers there are plenty of people who prefer a direct flight for both the convenience and time savings.
You may be able to find more stats here.

if by "the Philadelphia area", you mean EWR, then I would agree with you. PHL doesn't even show up on the misery map. http://flightaware.com/miserymap/KEWR

I was actually referring to PHL (I departed a lot from KPNE) but more the fact that by the time you get in the air to actually go anywhere out of the area you are more than likely going to contend with the NY Bravo or the DC Bravo space (or have to avoid them) and you will be there quickly if you are in a plane of some speed.

I may try and answer for Bologna which could be a similar case as for other supposedly non busy airports. (I am from Bologna myself!)
I think the reason is that even though the airport is not on the top 30, Bologna itself is one of the busiest economic hubs in Italy. For example from here we have factories like Ferrari, Maserati, Lamborghini and Ducati which are all in the radius of 30 km from the airport.
So if it does not make sense passenger-wise I think it does commercially.
There is also another theory which I have heard from FastJet management (Low cost regional carrier in Tanzania) which serves neighbouring countries. Sometimes you do not have to serve where there is business. The simple fact that you are opening a new route will automatically create business. As an airline YOU are creating the business for many other sectors. This is very true for example for Harare where now, with FastJet there are a lot of people flying into Dar es Salaam to pick up used cars shipped from Japan. This was not happening before but it is now a reality and their flights are fully booked for months from Harare to Dar es Salaam. On the other way (DSM-Harare) there are not many passengers but the pilots are telling me that the plane is fully laden with cargo!
So sometimes it seems that a route is not profitable but probably because no one is doing it. The moment you open it up, BANG! like magic new businesses start to flourish!

Eurostats provides information EU air passengers information, it details air passengers transport Each of EU countries and their main airport partner.
Based on the above link, there is the passengers information between Dubai and Newcastle/Prague.

Departure meanes the flights from the cities to dubai, and arrival stands for the flights from dubai to the two cities.
As you can see, the load factor for Newcastle and Prague is around 70%, both are lower than Emirates 79.6% average. Newcastle are serviced by 2-class B77W while Prague is serviced by 3-class b77w/a388.
Load factor of both cities are from 50% at low season to 80& at high season. Although load factor of Prague route is lower than Newcastle in 2015, please note that at that time Emirate ran this route by A388 instead of B77W.
PS: The nearest airport to Bologna which Emirates serves is Venice, not Milan,although the fastest way between 2 airports and Bologna are almost same.

haha - Yes, Venice is indeed much closer to Bologna than Manila. Several thousand miles closer. :)

Don't forget that aircraft size and link capacity are only loosely related, because it also depends on how many flights there are.
For example in case of Prague, I counted 6 departures to Frakfurt and 7 to Amsterdam a day, while only 2 to Dubai (the Emirates B77W and one SmartWings B738). So while the flights to Frankfurt and Amsterdam are all smaller planes (A319, A320, A321, to AMS some are even just E190), the capacity to both those destination is about double that to Dubai.
For the closer hubs, it makes more sense to fly smaller planes more often, because it can be more easily scaled (e.g. swapping A320 for A321; they don't even have to change the crew for that) and because it allows shorter transfer times, which the passengers obviously prefer.
However Dubai is much further and the small aircraft are less practical for that distance and for long trips, the stopover is smaller fraction of the travel time, so the passengers are more willing to accept it. So Emirates flies just once per day and uses large aircraft.

[C]ouldn't the people living around Bologna take a train to Milan to get to Dubai... ?

Maybe. But even if they can, it's much less convenient. By the time you've factored in taking a train from the outskirts of your city to the centre, waiting for the connection, taking the one-hour train, arriving earlier than you wanted to because of the schedule, and allowing extra time in case the train's late, that can easily be 2hrs actual travelling.
Also, the time of the first train of the day might prevent you from taking morning flights. I used to use my local airport and travel via Amsterdam instead of taking a "75-minute" train to the regional airport and getting a direct flight. Not only was the 75-minute journey more like 135 minutes (because I had to get a local train to the city centre and wait for a connection) but, also, the first train of the day was at 0615, so it was impossible to be at the regional airport before about 0830, so you wouldn't want to take a flight before about 1030.
Yet another problem is that, if my trains had been late, I'd have been at the mercy of my travel insurance company and airline agreeing that I'd made reasonable efforts to get to the airport on time and not charging me to rebook the flight. If the shuttle flight to Amsterdam was late, it was unambiguously the airline's responsibility to get me to my destination.
Finally, Emirates aren't really about people flying to Dubai. Rather, they want to be a hub for people flying via Dubai. Flying to many different airports makes Dubai a more attractive hub, for example for people flying between Europe and the Asia/Pacific region. You probably don't care what hub you fly through but being able to go from your local airport rather than the regional one can make a big difference.

I don't think you have to dig much deeper that the fact that Emirates is exclusively an international carrier; and they have decided to standardize their fleet on the 777 and the A380 - this is actually more economical for them since they are able to get cost savings by only servicing two kinds of airframes.
Overall for them - it makes sense to standardize on these two kinds of aircraft, which means that no matter where they fly - it will either be on a 777 or a A380, no matter what the load ratio is.
This means you have some silly routing - such as flying an A380 from Dubai to Kuwait, a route exclusively serviced by the 737/A320/A321 family by every other carrier. Even Eithad (the UAE's national airline) flies this route on the A320.
For Emirates, when speaking of operations at their scale, it makes sense for them to fly a standard configuration, with a standard crew layout to all destinations. In fact, I would hazard a guess that most airlines would love to do what Emirates is able to, rather than having to service, train for and maintain different kinds of aircraft.

For short haul, you could refer to the model that Southwest adopted a few decades ago, to only fly 737.  Good answer.

I guess one of the reasons for this wide-body use is because this is the primary aircraft for medium-haul routes in the Emirates Network. The 777 for Emirates is the workhorse of the Emirates airline and it has contributed to it's success. But in reality I do agree with you. Many Emirates routes that I have seen on YouTube do not have full aircraft which cannot be economically viable. But I guess this is why Emirates are so careful of assigning the A380 to a route. An example I can think of is Zurich which up till recently was operated by a 777. This is because the A380 is such a huge plane that it is only viable if the flight is packed. The 777 on the other hand is an aircraft that is used for a plethora of routes by Emirates. Reasons for this could be that it is the only widebody aircraft Emirates can use for this route.

Your last phrase - I don't find it particularly convincing nor accurate. Especially owing to what you can see here (https://en.wikipedia.org/wiki/Emirates_fleet), where it is reported that Emirates has 18 Airbus A330-300, which is somehow smaller than the 777. So, one thing is saying that an airline DOES NOT have a smaller aircraft, and a completely different one is saying that it does not have ENOUGH of them.

I'm very sorry if I my comment was not accurate but it is just my opinion. I have flown on Emirates' old A330's and the A340's which are very old and may not be suitable for this European route. Although Emirates does operate the A330 to Newcastle occasionally I do believe that Emirates would much rather operate a 777 to a European destination compared to an A330. I do apologize if it did not come across as accurate. This is just my opinion based on my experience on board the Emirates Fleet

No problem buddy, thank you for your contribution anyway!

It's very simple. Emirates is HEAVILY subsidized by the government of UAE. They are privately held by a government investment corporation which means any data on yield, load factors, PRASM, CASM, or profits are not to be trusted. They are trying to flood certain markets with capacity in order to kill competition and gain market share. It's a age old strategy in the aviation world, but it tends to not to work out so well in the long run. Its a great idea until you have a bunch of other airlines trying to do the same thing, then you end up with a HUGE glut of capacity and fares in the dumper! Eithad, Emirates, Saudia, Quatar, and Turkish airlines all seem to be flooding their markets with capacity, we shall see which country has the largest appetite for loss.

This statement doesn't even make sense - UAE's national airline is Etihad, not Emirates. Emirates is the airline for Dubai, which is an emirate in the UAE. Being owned by the government doesn't mean it is subsidized by the government. in fact, just like any other major airline Emirates has to take out sizeable loans for airport and fleet expansions.

This answer could be improved by citing sources.

You should provide sources, links and references to improve your answer and provide further readings and context.


text:
Can a helicopter operate continuously in a small, enclosed, sealed environment?
Many years ago I had an interesting discussion with a friend (while drinking). We were discussing what would happen if a helicopter was placed into a sphere of some size (slightly larger than the helicopter, a few times larger than the helicopter, etc.). Assume the sphere is filled with air at standard temperature and pressure, and there is standard 1G gravity pulling in one direction.
Can the helicopter maintain flight?
I believe it might, for a very short time, until the air starts circulating in a (relatively) stable manner, causing the "natural flow" of air to be already descending when it encounters the rotor disc, therefore reducing lift to nearly nothing.
I'm curious what an expert might think. If this is off-topic, mark it as such and I'll delete the question. Adding more useful tags I don't know about might also be helpful. :)

I suppose this might also apply to a helicopter trying to fly within a hanger.

No, it won't fly unless the sphere is so large that recirculation of the air is not a problem since, as you rightly say, it will fly for a short time until the air above the rotor is already descending and therefore, the angle of attack is reduced such that not enough lift to maintain flight is produced.  I don't have the maths required to figure out how big the sphere must be for a given helicopter but some masochist might posit one to gain a few points :)

The other question remains, would you starve the pilot and engines of breathable/combustable oxygen before the airflow patters became an issue?

@Simon: So the answer is the rotor blades will stall?

I never thought of the engines using up the oxygen, etc. I only really considered the aerodynamic aspects. I think that the engine quitting due to lack of air spoils the fun and could be disregarded. Interesting thought.

I don't think so.  As the air is forced out then backup by the sphere, it will increasingly speed up so a loss of lift will be experienced and the helicopter will sink to the floor of the sphere.  In fact, thinking about it, the air will already be circulating before it lifts off!  Oh no, it's a treadmill question!  I now vote that it cannot even lift off unless the sphere is sufficiently large that recirculation does not occur.

See the related question Can an aircraft or helicopter run into its on wake vortex?.

Speaking of treadmill debates: the Mythbuster episode 'Birds in a truck' is quite relevant. I think they tested it with a drone, and the result is yes, you can fly something in an enclosed space if it's relatively large compared to the thing you're flying. Furthermore, the weight of this space+heli will not change when it takes off due to the pressure differential you create.

Look up "vortex ring state" and "settling with power".

@Riccati Those are totally different phenomena.  They occur when the helicopter descends into it's own vortex.  The end result is the same but they are not caused by accelerated air being drawn into the disc from above, as would happen here.

Quadcopter in a (dry) shower stall?.. I see a Mythbusters episode...

A helicopter develops lift by accelerating air downwards through its rotors.  This relies on the air above the rotors being slow enough for the rotors to accelerate that air enough to provide sufficient lift. When hovering in still air, the incoming air has zero velocity relative to the helicopter. While of course the air is conserved, in a large volume of air, the downwash is able to diffuse much more, and much of it does not immediately circulate back up above the helicopter.
If the helicopter were enclosed in a sphere, the smaller the sphere, the less the air would be able to diffuse. The downwash would circulate back to the top of the sphere, where the rotors would take that air in again. The rotors would be less effective at accelerating the air that is coming in with significant velocity, just as a propeller develops less thrust with increasing forward speed. Successful hover would depend on the helicopter being able to develop lift at a rate of circulation where the air can slow down enough for the rotors to be effective.
This seems like a experiment manageable enough that someone could try it at home...

@Thesis yes, I would also add Simon's qualification of unless the sphere is sufficiently large that recirculation does not occur. There will be some sphere large enough that the losses equal the energy added by the helicopter.

A serious danger to helicopter flight is flying in a vortex ring state, causing a stall.

Essentially, the helicopter descends into its own downwash. When the condition arises, increasing the rotor power merely feeds the vortex motion without generating additional lift

Several helicopters have crashed as a result.
This state would be very quickly established for a helicopter in a confined container.

I think I disagree.  In vortex ring state, the helicopter descends into it's own downwash which reduces the velocity of the air accelerated downwards, causes an upflow through the hub and therefore reduces lift as the blade stalls from the root.  Recirculation is a different phenomena.  With recirculation, the problem is that the inflow from above accelerates downwards.  The incipient condition of VRS is an upflow through the hub.

Think of it a different way, VRS can ONLY happen when the helicopter descends.  Recirculation can, and does, occur in descent, climb or hover, e.g. when hovering near a building.

I'd love to accept this answer, because it makes sense (maybe confirmation bias on my part? :)  and because of the cool graphic (attribution?). I'm going to let this one ride for a day or two, though, to see if anything else interesting is posted. Also, hopefully my question doesn't get closed - 2 votes at the moment! heh...

@Steve: the image was released into the Public Domain by Xmnemonic (James Cho) according to WikiMedia.

Indoor model helicopters would not be able to fly if the answer were no.
Of course it can, but the enclosure must be big or small enough to avoid a toroidal vortex from developing around the rotor. To summarize my answer, three conditions make it possible:

A very big enclosure which allows enough forward speed so the helicopter never flies in its own wake,
a very low ceiling or
a very narrow enclosure.

Case 1 is trivial, so I dwell here on case 2: If you have flown an indoor model helicopter, you probably know that it is not advisable to come too close to the ceiling: The helicopter will become unstable and will be sucked right into it. This is caused by the ground effect (or better ceiling effect in this case): The efficiency of the blades increases the closer they are to a horizontal surface and the helicopter needs less torque for the same lift. Once the rotor head is touching the ceiling, you need to cut power almost to zero to free it again. The same effect can now be used to fly in the constrained space because it will prevent the toroidal vortex of the vortex ring state from developing.
Now the explanation to case 3: If you insist on not touching any surface, the vortex will soon develop and reduce lift. How long you can hover depends on the air volume, and there is a minimum when the diameter of the enclosure is approximately twice the rotor diameter. Once the diameter becomes smaller, the vortex will again be inhibited, and when the enclosure is small enough the rotor will look like a fan in a duct. Now again less energy is needed for lift - just enough to maintain the necessary pressure difference through the rotor disc.
I should add that this solution will best work with a co-axial rotor and no tail sticking out at one end.

Interesting. I never considered the 3rd case where the helicopter essentially behaves as a pump. Yes it should work because we know some axial compressor designs work (with some leakage). The narrowness essentially stops recirculation and the disc essentially becomes a very inefficient piston. :D

In the movie 1982 Deadly Encounter,  if my memory serves me correct, there is a scene where a Hugh 500 flies inside a large hangar. No CGI in ‘82, don’t believe any special effects were used, so yes indoor flight possible. My thought being the accelerated air above rotors would somewhat balanced by ground effect.

Welcome to AviationStackExchange. Please give a time stamp of the stunt you just mentioned. The only thing I could find that was similar was a stunt where the Hughes 500C Loach was chasing a Aérospatiale SA 315B Lama through a long, open, barn-like enclosure with no walls. It only had a roof and roof supports. The vortex ring state described in this question would not be realized for two reasons. 1) The air would not be able to recirculate above the rotor blades due to the open sides. 2) The aircraft never stopped forward motion. Without stopping, they would not get caught in the vortex.

You are correct, I went back and looked for the movie on Youtube my memory was faulty, yes the stunt was done flying though an open walled structure, not really “indoors”.   However  at the beginning of the movie he fires his little Hughs and flies it out hanger front of the hanger , and then plays a little kick the can with local Mexican boys , by hitting the can with one of the skids, not sure about that stunt, but the rest of the film has some amazingly skilled flying , dangerously so.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is Iqaluit Airport closed?
After seeing this question (and its answers):

Why did the Swiss International Air LX40 (a 777-300ER) emergency land at Iqaluit airport?

my interest in Iqaluit (and its airport) was piqued.  But, the satellite/aerial view in Google Maps shows the single runway at YFB (ICAO: CYFB) closed (big "X"s painted on the runway).  Refer to below screenshot (Google maps satellite view):

Best I can tell, this satellite imagery was taken recently ("Copyright © 2017...")
Is Iqaluit Airport closed?

If it is, I sure as heck can't find a NOTAM saying so...

Note that the copyright date on the images does not necessarily tell you when the image was taken, only when the image was added to the database and posted online.

At the time of the imagery, it appears the airport was undergoing major renovation, now completed at least insofar as the runway is concerned. See iqaluit-airport-s-runway-gets-a-facelift-as-construction-completed. During the reconstruction they kept a minimal portion of the runway open for operations, enough to bring 757s in but not enough to get 767s in.
If you look at the image, note all the construction activity and also the parked aircraft. Note that the Xs are on the right side of rwy 34, and leaving the left half of the runway open. Farther down the rwy the Xs are in the middle, so I believe the image was taken while they were reconstructing the rwy while leaving enough of it usable for operations.

This accident description (accident on July 8th, 2015, runway excursion on half width runway) talks about closure of half the runway and related Notams.

@mins Wow. I bet that crew never forgot to check the NOTAMs again...

@reirab, yep, read and understand that "100 ft" closed was for width, not length! But it happened again three days later.

@mins: NOTAM: READ THE F*!%ING NOTAMS.


text:
Was there any Hawker Trident installed cockpit voice recorder before BEA Flight 548 incident?
After BEA Flight 548 incident in June 1972, all British-registered airliners have mandatory cockpit voice recorders. The TV series Mayday claimed no voice recorders were installed in Hawker Tridents before the report of the incident was released.
9 months before BEA Flight 548, a Chinese Air Force Trident 1E (AP-ATL) crashed in Mongolia. Lin Biao, the second-in-charge in China, was killed as well as his family members in the incident.
The incident itself is still mysterious, but some source claimed that there were voice recorders in the cockpit and the chat inside the plane was recorded.  Many sources cited that the Chinese officers did not know the black box was installed, so the voice recorder was only installed by either Pakistan International Airlines (previous owner of the airliner) or by the manufacturer.
The question is : Were there any Hawker Trident installed cockpit voice recorder before BEA Flight 548 incident?

It doesn't appear that CVRs were installed in any Tridents before the BAE 548 accident.
The accident report noted that CVRs are installed in some British Aircraft, but stays silent on the Tridents:

This, at least as far as CVRs is concerned, we do not regard as
  satisfactory. ... They are fitted as standard equipment to all BOAC's 747s and most large United States transport aircraft.

If any of the Tridents had CVRs, the report would've surely mentioned it. The Chinese Tridents didn't appear to have CVRs long after the accident. In fact, the accident report of a Trident 2E in 1988 notes,

The  aircraft  was not equipped, neither was it required to be equipped, with a cockpit voice recorder (CVR).

Based on these, it does not appear that any Tridents were fitted with CVRs before the accident.

authors: Роман Кошурников


text:
Is there any legitimate reason for adding momentary power when descending at idle with full carburettor heat on?
Scenario: While demonstrating a simulated engine failure emergency landing a flight instructor puts on carburettor heat and reduces the throttle to idle of a small single engine Cessna. After a couple of minutes descending to the simulated emergency landing site, the CFI adds throttle "to clear the plugs" for a few seconds, then brings it back down to idle to complete the demonstration.
Is this is a legitimate thing that needs to be done for safety?
I've seen several pilots do this, and to me it always seems like cheating, because they are coming in a little short of their landing target.

How much plug fouling can occur in 2 or 3 minutes of idle with carburettor heat at low altitude?
How much good can 3 to 4 seconds of full power do?
Is there something else about this that I'm missing? (I couldn't find anything on this after a brief Google search).

My flight instructor made it no secret that I could stretch the engine warm a few seconds longer if I was going to be short. Of course, how prepared I am for a real emergency is another question.

straight out of the Airplane Flying Handbook, pp 9-4

Operating the engine at idle speed for any prolonged period
  during the glide may result in excessive engine cooling, spark
  plug fouling, or carburetor ice. To assist in avoiding these
  issues, the throttle should be periodically advanced to normal
  cruise power and sustained for a few seconds.

This procedure is common during emergency descents or steep spirals to prevent the engine from cooling off too much.  If the engine mixture is excessively rich, spark plug fouling can occur.  Fouling can be cleaned off the plugs by running the engine at Cruise power settings with a properly leaned mixture in about 10 or so seconds.

Excellent. Thank you for the reference. I wonder if there is any authority on what the Flying Handbook means by "prolonged periods."

@Devil07 FWIW, I've personally experienced plug fouling when taxiing for a couple of minutes with a rich mix. It doesn't take long. After running it up to 2k RPMs for ~30 seconds and testing again, all was fine.

Also, if the engine actually fails for some reason, you may not note that due to propeller windmilling. In that case, the simulated emergency turns in a real one, and the actions taken by the instructor/pilot may change. Giving momentary power to the engine ensures that it will be able to climb out in a go-around.

@ricardomenzer I think what you said (confirming power availability) is probably the most persuasive reasons for doing this.  I've talked to mechanics and "shock cooling" is a real thing, but unlikely to be encountered in actual idle gliding descent, carb ice isn't really an issue if you have carb heat on or its fuel injected, and plug fouling isn't an issue if you're leaned properly (plus mixture just continues to lean as you descend).

This practice is often referred to as "clearing the engine" and serves two purposes. The temporary change in power has a positive effect on clearing potential fouling of spark plugs, which are susceptible to lead-fouling, carbon-fouling and oil-fouling.
The second effect is to provide feedback to the pilot on the status of the power plant. Should the engine not respond favorably to a clearing power change, then the pilot is immediately made aware of that, and can either take corrective measures, such as increasing the power and leaning the engine to burn off or dislodge deposits. Alternatively, if low to the ground on approach, the pilot is aware that there is a potential power plant issue and can plan accordingly should there be a need to alter his path.
This maneuver is best practice in a light piston powered aircraft during certain training maneuvers, such as simulated engine out procedures.
Furthermore, while notions of best practice vary, there is general consensus that extended low or idle power glides of one minute or longer should have an clearing power change.  This power change may only last a second, and if so executed, has a negligible impact on the glide path of the aircraft.
Because aircraft such as helicopters, tend to run at high power settings in all phases of flight, this maneuver does not apply except in situations such as extended auto-rotation practices.  Also, this maneuver has little benefit to turbine powered aircraft, and is not indicated for extended glide in aircraft so equipped.
So bottom line, clearing the engine has a preventative effect in that it provides a moment of power to alter power plant conditions which could lead to unreliable operation. Secondarily, if there is a degradation in the performance of the power plant, it provides the pilot notice of that, so that the pilot can situationally evaluate options and act accordingly.

I think you're a word in "simulated emergency out procedures", but I'm not sure if "emergency" should be replaced by "engine" or if "emergency out" should be "emergency engine-out".

@MichaelKjörling, good spot, and I have edited accordingly.  Thank you.


text:
What are flight check operations?
KDCA/DCA is currently experiencing delays in both arriving and departing aircraft, and several sites list variations of "Flight check operations" as the reason.
The FAA itself provides the following status for DCA (which I'm guessing is where all the other sites pull from):

Due to OTHER / FLIGHT CHECK, there is a Traffic Management Program in
effect for traffic arriving Ronald Reagan Washington National Airport,
Washington, DC (DCA). This is causing some arriving flights to be
delayed an average of 20 minutes. To see if you may be affected,
select your departure airport and check "Delays by Destination".

At a commercial airport, what is a Flight Check / what are flight check operations? Why would they be implemented?

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How to identify an aircraft from its NC- N-number?
I have the numbers from the tail NC and then down is 4686N. Its a single wing prop driven multi seat aircraft. I am unable to locate it on the federal site, hoping I can get some info here again. Thanks, Ron

What does "tail NC and then down is 4686N" mean exactly? The confusing part is the "then down" part, is the number on two lines? Is it "NC" (next line) "4686N"?

Are you able to post a picture of it, or a link to a picture? And is it a US aircraft?

The top of the tail section has NC and just below that 1 number after another 4 then 6 then 8 and so on.

I'm afraid that attaching a photo seems to be more than I am able to do! It's not just a matter of attaching a photo from my collection. OR is it?

@Pondlife "NC" is an older FAA registration type. I had a question about them before.

As I understand it ...N means American & C means Civilian. At least I hope so.

Based on the re-edit, it would be a duplicate of this question.

You should be able to post a photo from your collection. It will be uploaded to the SE image sewer and linked to so it won't go broken. If you edit your question there should be a camera icon to add an image

Single wing prop driven multi seat aircraft? Not sure what you mean by this. A quick search on the FAA registry indicates it's a Cessna 414A.
Also, the style of tail number with NC is older, Wikipedia has an explanation of the various styles of aircraft identifications.

An older aircraft (registered before 31 December 1948) may have a second letter in its identifier, identifying the category of aircraft. This additional letter is not actually part of the aircraft identification (e.g. NC12345 is the same registration as N12345).

An older aircraft with the same N-number on the FAA registry is the BT-13.

Welcome to Aviation.SE!

Thanks so much for the lead to the BT-13. I will look it up now. Back to your other comment this aircraft not only had the NC12345 but it did have the numbers first and the N designation last. Does that affect it in any way?

Thanks to all, it looks like my photos are of a BT-13 as suspected  earlier.

FAA registry entails that in the United States and most of northern america, aircraft are classified and registered into the FAA database via something known as an "N-number" to FAA specialists, and to their website. For every American-made/American registered aircraft, there is a respective N-number for it. For example, there are several different occurances of patterns in the N-number system in North America, you can have a registry with N457FR, where there are two letters on the end of the registry, or you can also have only one letter, and eventually only five numbers and only the "November", of which, five-number registry combinations are not as frequent in the United States, but can be found sometimes in the Caribbean and Canada. It also may be worth stating that the letters at the end of a registry can also be a direct effect of the aircraft's owner, date of purchase, or airline. For example, the regional airline company, Air Wisconsin, a subsidiary of US Airways (now American) have the letters "AW" at the end of each of their aircraft's registry. Furthermore, aircraft that are private and are not owned by any airline cooperation of such may have their aircraft's callsign be its registry. FedEx and most small Private Jet charter services have been well-known for doing this. You can find almost any aircraft registry on flightaware.com or by simply googling the callsign or registry.

Thank you Eric, it gives me additional areas to search into for other photos that I have.


text:
What is the derivation of 15 and 11.3 used for estimating pivotal altitude?
Pivotal Altitude Explained: Teaching eights on pylons the easy way at AOPA repeats a common formula for pivotal altitude.

To estimate pivotal altitude, square the groundspeed and then divide by 15 if you use mph, or 11.3 if you prefer knots.

Where do the 15 and 11.3 magic numbers come from?

A possibly surprising result is even airplanes as different as a humble Cessna 152 and a Boeing 747, if able to fly the same speed in the same conditions, would use the same pivotal altitude. The airplane’s velocity and acceleration due to gravity are the only factors in determining pivotal altitude. Detailed derivations by John S. Denker and by ERAUSpecialVFR (13:57 YouTube) are included below.
The exact formula for height above the pylon is
$$h = \frac{v_{air}\cdot v_{gnd}}{g}$$
where $v_{air}$ and $v_{gnd}$ are velocities relative to the air and ground, and $g$ is acceleration due to Earth’s gravity. This shows that the common approximation of squaring groundspeed is the calm-day special case.
Assuming we want to know $h$ in feet, we need to connect the building blocks, namely the units of measure, appropriately. Given that $g$ is 32.17405 ft/s² (that is speeding up by 32-ish feet per second every second), compatible velocity will also be denominated in ft/s. To see why, you can think of the units as canceling out, as in
$$\frac{\frac{\textrm{ft}^2}{\textrm{s}^2}\equiv v^2}{\frac{\textrm{ft}}{\textrm{s}^2}\equiv g} \Rightarrow \frac{\textrm{ft}^2}{\textrm{s}^2} \cdot \frac{\textrm{s}^2}{\textrm{ft}} \Rightarrow \textrm{ft}$$
At least in the airplanes I fly, the airspeed indicator displays knots or miles per hour. The conversion factor from knots to feet per second is $\frac{6{,}076}{3{,}600}$ because there are 6,076 feet in a nautical mile and 3,600 seconds per hour. For statue miles to feet per second, the factor is $\frac{5{,}280}{3{,}600}$. Remember that the formula for pivotal altitude has two velocity factors, so we must square the conversion factor.
$$d_{mph} = 32.17405\ \textrm{ft}/\textrm{s}^2 \cdot \Biggl(\frac{3{,}600\ \textrm{s/hr}}{5{,}280\ \textrm{ft/SM}}\Biggr)^2 \approx 14.9569\ \textrm{mph}^2/\textrm{ft}$$
and
$$d_{kts} = 32.17405\ \textrm{ft}/\textrm{s}^2 \cdot \Biggl(\frac{3{,}600\ \textrm{s/hr}}{6{,}076\ \textrm{ft/NM}}\Biggr)^2 \approx 11.2947\ \textrm{knots}^2/\textrm{ft}$$
Then performing the dimensional analysis to see that the units of measure fit in the knots case, for example:
$$\frac{\textrm{NM}^2}{\textrm{hr}^2} \cdot \frac{\frac{\textrm{ft}^2}{\textrm{NM}^2}}{\frac{\textrm{s}^2}{\textrm{hr}^2}} \cdot \frac{\textrm{s}^2}{\textrm{ft}} \Rightarrow \textrm{ft}$$
That is, the squared airspeed converted to $\frac{\textrm{ft}^2}{\textrm{s}^2}$ divided by the acceleration due to gravity yields a quantity in feet.
Thinking of the magic numbers in the denominator may show more clearly what’s happening. In the case of knots, $\frac{1}{11.3}$ is around 0.0885 feet per knots squared. This means approximately the same as 9 feet per knots gained or lost, per 100 knots (because 9 ≈ 0.0885 × 100). Likewise for statute miles, the pivotal altitude changes by about 7 feet per mph airspeed change, per 100 mph the airplane is traveling. In either case, given two airplanes where one is flying twice as fast as another, a unit of airspeed gained for the faster will have twice the impact on its pivotal altitude as compared with its slower counterpart.

5. Derivation of the Nifty Formula

We wish to derive the nifty formula for the altitude required during a turn on pylon in the presence of wind. We will be using the following quantities:

$R$, horizontal position vector, from pylon to aircraft
$h$, height above the base of the pylon
$V_{Gnd}$, velocity relative to the ground
$V_{Air}$, velocity relative to the air
$W$, wind vector = constant, independent of time
$a$, acceleration vector = derivative of $V_{Gnd}$

or (equivalently) = derivative of $V_{Air}$

$g$, acceleration of gravity

Assumption: We assume constant $\lvert V_{Air}\rvert$ i.e. constant airspeed.

The velocity relative to the air, $V_{Air}$, is perpendicular to $R$. That is, $$V_{Air} \cdot R = 0 \tag{4}\label{eq4}$$ This is required by the rules of the game. The heading is perpendicular to $R$ because the wing is pointing at the pylon, and the airspeed vector is parallel with the heading because we require coordinated flight (zero slip).

The acceleration $a$ is antiparallel to $R$. This is required by the rules of the game, since the wing is pointing at the pylon. That means the horizontal component of lift is pointing at the pylon. Meanwhile, all other forces add up to zero in accordance with the constant-airspeed assumption. Because $a$ is antiparallel to $R$, we have:

$$a \cdot R = −\lvert a\rvert \lvert R\rvert \tag{5}\label{eq5}$$

We will be interested in what happens to all these quantities after some time $\Delta t$ has passed. Time-stepping the equations of motion gives us: $$
\begin{align}
\textrm{new}\ V_{Air} & = \textrm{old}\ V_{Air} + a\Delta t \\
\textrm{new}\ R & = \textrm{old}\ R + V_{Gnd} \Delta t
\end{align} \tag{6}\label{eq6}
$$

Combining equation $\eqref{eq6}$ with equation $\eqref{eq4}$ gives us the time-delayed version of equation $\eqref{eq4}$:$$(V_{Air} + a \Delta t) \cdot (R + V_{Gnd} \Delta t) = 0 \tag{7}\label{eq7}$$

Multiplying out equation $\eqref{eq7}$ gives us: $$0 = V_{Air}\cdot R + a\cdot R\Delta t + V_{Gnd}\cdot V_{Air}\Delta t + a \cdot V_{Gnd}(\Delta t)^2 \tag{8}\label{eq8}$$ The first term vanishes in accordance with equation $\eqref{eq4}$. The second term reduces to $\lvert a\rvert \lvert R\rvert \Delta t$ because of equation $\eqref{eq5}$. The fourth term is negligible in the limit of small $\Delta t$.

Rearranging the remaining parts of equation $\eqref{eq8}$ gives $$\lvert a\rvert = \frac{V_{Air} \cdot V_{Gnd}}{\lvert R\rvert} \tag{9}\label{eq9}$$ This tells us the magnitude of the acceleration. The direction is antiparallel to $R$ as mentioned [elsewhere]. So now $a$ is fully determined, since we know its direction and magnitude.

As usual, when the aircraft is properly banked toward the pylon, the geometry of the situation is shown in figure 3 [shown below]. In this geometry, the law of similar triangles tells us $$\lvert a\rvert = \frac{h}{\lvert R\rvert} g \tag{10}\label{eq10}$$

Combining equation $\eqref{eq9}$ and equation $\eqref{eq10}$ gives us the nifty expression for the required height at any point during a turn on a pylon:$$h = \frac{V_{Air} \cdot V_{Gnd}}{g}\tag{11}\label{eq11}$$ You can readily verify that this reduces to the conventional expression for the pivotal altitude in the no-wind case.

Physics of Flight - Pivotal Altitude - Lesson 6 by ERAUSpecialVFR

Figure created with Khan Academy

$\sum F_y = 0 \Rightarrow L \cos\theta = mg$

$\sum F_x = ma_c \Rightarrow L \sin\theta = \frac{mv^2}{R}$ (centripetal force)

$\frac{L\sin\theta}{L\cos\theta} = \frac{\frac{mv^2}{R}}{mg} \Rightarrow \tan\theta = \frac{v^2}{Rg}$

$\tan\theta = \frac{h}{R} = \frac{v^2}{Rg} \Rightarrow h = \frac{v^2}{g}$

$\therefore PA = \frac{GS^2}{g}$

$\begin{aligned}
  PA = \frac{GS^2}{g} &\approx GS^2\cdot\frac{\left[\left(1\frac{\textrm{nm}}{\textrm{hr}}\right)\left(\frac{1.15\ \textrm{sm}}{1\ \textrm{nm}}\right)\left(\frac{5{,}280\ \textrm{ft}}{1\ \textrm{sm}}\right)\left(\frac{1\ \textrm{hr}}{3{,}600\ \textrm{s}}\right)\right]^2}{32.17\ \textrm{ft}/\textrm{s}^2}{} \\
                      &\approx GS^2\cdot\frac{(1.687)^2}{32.17} \approx GS^2\cdot\frac{2.845}{32.17} \approx \frac{GS^2}{11.3}
  \end{aligned}$

If the Vair is constant and there is significant wind at altitude, Vground will vary throughout the turn. So... is the approved solution to hold bank constant & vary altitude throughout the turn, or to hold altitude constant & vary the bank angle to adjust for wind?

@RalphJ At any given moment, the airplane’s $V_{air}$ and $V_{gnd}$ will combine to yield a particular pivotal altitude, so the answer is to hold constant bank and vary altitude because $h$ varies as a function of the velocities, not bank.

After you have an understanding of the base formula to calculate your pivotal altitude and the units used, which is:
PA = V^2/g
That is...
V: tangential velocity in knots (AKA NM/HR)
g: the acceleration of gravity in feet per second^2
PA (or could just be h): pivotal altitude height in feet

It is a given that the output unit of distance must be feet because feet is the unit used on the altimeter (or at least every one I've ever used) which makes any other unit more or less useless to a pilot wanting to fly pivotal altitude based on the altimeter in feet.
The problem that the 11.3 conversion is solving is correcting, V in NM/HR to FT/S without having to write out the entire conversion each time and it bundles that conversion with division of V^2 by acceleration of gravity.
I wrote this answer despite the age of the question and thorough first answer because I feel that there is a missed point:

11.3 is the coversion of NM/HR to FT/S twice multiplied by the acceleration of gravity in FT/S.

The "long" way of writing this formula (after cancelling out tangent theta and mass leaving PA = V^2/g) is:
* Take V^2 and split it to V * V.
PA = V * V / g

I need to convert each V to FT/S since we will use NM/HR from the airplane's readings, so the expanded version is to write the conversions twice.
((V NM/HR * (6076.12 FT/NM / 3600 S/HR)) * (V NM/HR * (6076.12 FT/NM / 3600 S/HR))) / g

Well, that's a mouth full, so it can be re-written as:
(V NM/HR * (6076.12 FT/NM / 3600 S/HR))^2 / g
If it can be grouped by squaring, then you can split it squared, so we would have:
V^2 * (6076.12/3600)^2 / g
Since the conversion factor of 6076.12ft/3600S is a stand-alone fraction, you can take the reciprocal to the denominator (AKA flip it and move it to the bottom).
V^2 / ((3600/6076.12)^2 * g)
3600/6076.12 = 0.59248... which squares to 0.35104... (S^2/FT^2)
Since the decimal result of the squared conversion factor is now in the denominator with g, it can be multiplied against g to get a single number.
0.35104 * 32.2 Ft/S^2 (AKA g) = 11.30338...
The end result is a number that effectively bundles the division of V^2 by gravity with the double conversion factor needed of "one per velocity unit" making the output of KTS^2/11.3 be pivotal altitude in feet.
V^2/11.3 = PA (in feet)

To understand V^2/15 for MPH simply replace 6076.12 ft with 5280 ft in order to convert in statute miles instead of nautical miles.  Otherwise, the math and logic is identical.


text:
What is the breakout by service branch for FAA ATC specialists with military backgrounds?
For young people interested in air traffic control careers with the FAA and who view military service as providing a boost toward that goal, which branches are most and least likely to get them there? In other words, how do the branches of the U.S. armed forces compare by headcount of ATC specialists working for the FAA?

I would venture to say it's got more to do with the MO selected than the branch. My son is in the Army and the closest he gets to ATC is when they direct the pilots of the birds he rides in. A good friend spent time in the Army active and (activated) Reserves doing ATC.

@FreeMan Yes, MOS is implied in my question. How does the likelihood of landing an FAA ATC job for an Army 15Q compare with an Air Force ATC Operator, for example?

Ah, I misunderstood. Carry on... :)

One thing to keep in mind is that military ATC in the US is fairly standardized across services. It has to be. It would be incredibly embarrassing if there was an accident and the cause was determined to be differences in ATC procedures and phraseology. That means the training is essentially the same across services.

All military services in the US have Air Traffic Control MOS codes and training, except the Coast Guard. Army, Navy, Air Force and Marines all have it.
I don't know of any source of data that tells me if an ATC controller is a veteran, and of what branch of service. As far as I know, the FAA does not discriminate on the basis of which branch you were in when you were awarded the ATC MOS upon completion of training.

The FAA doesn't care which service an applicant was in. They only care about direct ATC experience. From a recent FAA job announcement for experienced controllers (closed Dec 9, 2018):

THIS ANNOUNCEMENT IS FOR CANDIDATES WHO HAVE MAINTAINED AT LEAST 52
  CONSECUTIVE WEEKS OF AIR TRAFFIC CONTROL EXPERIENCE INVOLVING THE
  FULL-TIME ACTIVE SEPARATION OF AIR TRAFFIC AFTER RECEIPT OF AN ATC
  CERTIFICATION OR FACILITY RATING WITHIN 5 YEARS OF APPLICATION WHILE
  SERVING AT:

a Federal Aviation Administration (FAA) air traffic control facility;    OR
a civilian or military air traffic control facility of the Department    of Defense; OR
a tower operating under contract with the FAA under section 47124

What they want is at least one year active ATC experience in full time separation of aircraft within the last 5 years.
The announcement also includes information on veteran's preference.

authors: Никита Емельянов


text:
Will portable Stratus ADS-B In receivers operate normally from the passenger cabin of a commercial airliner?
Are ADS-B In receivers such as Stratus or Stratux permitted to be used along with other portable electronic devices at cruise altitude on commercial airliners? Will they receive GPS and ADS-B signals in the passenger cabin to be able to track progress on ForeFlight, for example?

Source: Appareo

I doubt a Rapsburry Pi in a homemade plastic box will meet any FCC regulation (it could be really harmful, I'd not say that for other FCC/EU certified hardware that are anyway also prohibited).

@mins -- the Pi itself (bare board) is FCC certified (I doubt the FCC cares about a plastic box as the box is rather...transparent to RF unless it's conductively loaded or metallized in some way)

@UnrecognizedFallingObject: I meant certified for cabin use. Arc welders are also certified by FCC, you'll agree they may not be compatible with the equipment in electronic bays. The original certificate is void as Raspberry Pi has been modified to receive 1090 MHz. For programmable modules, firmware/drivers controlling the RF components need to be certified with the board. The result of shielding can make a difference in RF levels and certification class.

@mins -- I suspect that taking a FCC-certified board and adding a RF module to it (the ADS-B In receiver) that is also FCC-conformant should be OK (the Pi's internal RF guts aren't being tweaked in any way)

The receiver will work in the cabin but the reception is really poor. GPS will only work if it has enough satellites in view, so a window seat is best. The signal is severely attenuated by the windows.
I have brought ADS-B receivers with me on various flights but in my experience you will not get a proper ADS-B signal from aircraft further than about 20-30NM away.
Whether it is permitted or not depends on the airline and the country of operation.

I've brought my Stratus on several trips. Inside an airliner, you'll really only get signal if you leave the thing pressed against a window the entire trip. Otherwise, you probably won't even get GPS lock, forget about ADS-B. TBH, there really isn't a lot to see once you get further away from the airport.
No one has ever made a fuss about me using it, typically they are just more curious as they see whats on my iPad. Once I was sitting next to an off duty captain, once he saw what I was looking at we ended up chatting the entire trip.
So... generally it shouldn't be a problem, but you should always follow the direction and instruction of the flight crew, commercial or not.

Although not banned by the FAA, virtually all major air-carriers have company policies that prohibit anything that sends or receives a signal.
This would include GPS and ADS-B receivers.
Here is one example

Devices that are NOT permitted for use:
  [...]
  - radio receivers and transmitters

"radio" is unfortunately an ambiguous term.  Given the many airlines that both permit GPS receivers and WiFi onboard, I don't think it should be read as "anything that receives any EM signal".

Delta explicitly allows during all flight phases.  http://www.delta.com/content/www/en_US/support/faqs/during-your-trip/personal-electronic-devices.html.   Joe Mehaffey used to keep track years ago at http://gpsinformation.net/airgps/airgps.htm.  It's out of date, but I doubt the number has gone down significantly since 2010.

There's no problem with using an ADS-B receiver in an airline cabin.  The United restriction I'm sure was targeted more at VHF or Ham radio equipment which could be tuned to interfere with frequencies used in flight.  Interestingly enough, I have brought my flight bag with me and my Icom AC-24 handheld VHF radio onboard commercial fights (but never powered it up!) without any objections from the flight crew.


text:
What's the best way to see accident rates for a particular make/model of aircraft?
I'm looking for a simple way to get NTSB safety statistics for different makes/models of aircraft so I can answer questions like:

How does the Diamond Aircraft safety record compare to general aviation over the last 5 years? All time?
How does does the Diamond Aircraft DA42 safety record compare to general aviation?
What were the (statistically significant) safest aircrafts in general aviation over the prior 5 years? What were the safest jets?

These are examples of questions. I'm mostly wondering if there is a tool or website out there that can help you answer these sorts of questions, or help visualize the NTSB data.
Thanks!

You can search the NTSB's accident database here:
https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx
Results can be filtered by date, aircraft type, location, etc.
Another good reference source would be the General Aviation Manufacturer's Association.
https://gama.aero/
Their annual report publishes accident data on general aviation aircraft.  The organization may be contacted for further information on this subject.
https://gama.aero/wp-content/uploads/2016-GAMA-Databook_forWeb.pdf

Thx for the response! It doesn't look like the NTSB site gives you statistics on the accident rates through that query engine, just a list of accidents? I believe it could be calculated by doing the work in excel, but I was hoping someone had taken the time to generate some more accessible data visualization from it.

You might try here as well https://aviation-safety.net/wikibase/dblist.php?AcType=DA42


text:
FAA: May I log as cross-country a flight with two or more short legs?
Consider a hypothetical flight plan from Redstone to Cullman to Gadsden and back to Redstone. This flight would have legs in order of 26, 42, and 52 nautical miles.

14 CFR 61.1 provides

Cross-country time means—
…
(ii) For the purpose of meeting the aeronautical experience requirements (except for a rotorcraft category rating), for a private pilot certificate (except for a powered parachute category rating), a commercial pilot certificate, or an instrument rating, or for the purpose of exercising recreational pilot privileges (except in a rotorcraft) under §61.101(c), time acquired during a flight—
    (A) Conducted in an appropriate aircraft;
    (B) That includes a point of landing that was at least a straight-line distance of more than 50 nautical miles from the original point of departure; and
    (C) That involves the use of dead reckoning, pilotage, electronic navigation aids, radio aids, or other navigation systems to navigate to the landing point.

The original point of departure is Redstone Army Airfield, and Northeast Alabama Regional is farther than 50 nautical miles away. Would the entire flight count toward the cross-country experience requirements for a private pilot certificate, commercial pilot certificate, or instrument rating? Must the pilot fly the 50+ nm leg first?

Great question! Will you be turning off the airplane and getting out at either of the stops? I've always thought that because of 14 CFR 61.1(ii)(B), if one of the points is more than 50 NM from the original departure point, and you did touch-n-goes or stop-n-goes at the other airports it would all count as one flight, with multiple stops but if you stop and get out before you've done a 50NM leg, it's two different flights.

Wish I could find a direct reg or thing to substantiate the answer: I've always been told, as long as 1 leg(where you touch the ground at both ends) of the flight is 50nm, the whole flight can be counted as cross country. Doesn't matter the order.

@slookabill No, the requirement is to land 50nm away, not to fly a leg of at least 50nm (see aeroalias's answer). The point is to 'force' pilots to navigate, otherwise you could fly a 50nm circle around your home airport and claim it was a cross-country, but you would never have had to navigate or make any real decisions in the air.

Not to sound flippant, but if the CFR doesn't say you have to fly the long leg first, then you don't.   If they don't say you can't shut down and get out, then it's OK.  There are lots of pilots who read way more into the regs than what is actually there.

Related: https://aviation.stackexchange.com/questions/55825/what-defines-the-end-of-a-cross-country-flight-for-ppl-aeronautical-experience

From a 2008 FAA interpretation sent to E. Thomas Sisk:

… cross-country flight time is defined as time acquired during a flight that includes a point of landing that is at least a straight-line distance of more than 50 nm from the original point of departure, not the original point of any flight leg. There is no requirement that any specific leg must be 50 nm. Moreover, a cross-country flight may include several legs that are less than a straight-line distance of more than 50 nm from the original point of departure. Nevertheless, at least one leg of the cross-country flight, however long by itself, must include a point of landing that is at least a straight-line distance of more than 50 nm from the original point of departure (i.e. of the flight, not of that particular leg).
Given the above analysis, the answer is each cross-county flight used to meet the aeronautical experience requirements under 14 CFR §61.1 (b)(3) must include one leg that includes a landing that is at least a straight-line distance of more than 50 nm from the original point of departure.

From the above, it is pretty clear that the order of flying does not matter and you can log the whole flight.
Also, see this AOPA response.

Yes you may log the whole "flight" as a cross-country flight.  And maybe some additional flights before and after the specified "flight", if you feel the urge to do so.  It's pretty much entirely up to your personal discretion.  For more see related question What defines the end of a "cross-country flight" for ppl aeronautical experience purposes and for general logbook purposes? .
As soon as you are reach the point in your training where you are capable of flying to a point 50 miles away, be sure to do so.  (Need not be a non-stop flight.)  All further hours accumulated after (or before) that point in time can be considered part of one long cross-country flight, lasting weeks, months, or years in duration.
If you decide to use this strategy, it might be wise to occasionally (say once a month or at least once per year) pass through a point that is at least 50 miles away from the point where the majority of your flights originate.  Just so no one can say you are trying to stretch the spirit of the regulations.


text:
How often does a pilot ask ATC for a repeat?
How often does it actually happen?
Also, is it fine to ask them to slow down if it’s hard to understand, for example, due to a heavy accent?

One would certainly hope it happens 100% of the time where there's any chance of confusion or misinterpretation. Reality is far less than that, then bad things happen.

I just ask my audio panel. But it happens plenty and as long as its not a super busy Class B Airspace the controllers dont really mind.

Isn't the real trick that the pilot repeats the essential information? If so, the ATC would realize that the readback is not correct and trigger the repeat itself. Of course when the pilot could understand nothing, he/she can't repeat properly.

How often is hard to quantify, but in general I would suggest the answer is all the time.
ATC is there to help you, as a service to you as a pilot. Sometimes out of necessity things are said quickly and it is the nature of the beast that sometimes some information is missed, or unclear. NEVER feel unable to ask for repeated information, or clarification if the information is unclear or ambiguous. Better to take up some extra airwaves than make a mistake!
If the information was delivered too fast and/or some was missed, be specific with what information was missed. This is preferable to asking for all the information to be repeated. A typical scenario might be

ATC: G-ABCD, Runway 22 in use, QNH <unintelligible>, taxi holding point Delta 2 via Apron, Alpha and Delta, giving way to the Cessna now entering the Apron.
G-ABCD: Runway 22, taxi to holding point Delta 2 via Apron, Alpha and Delta giving way to traffic on the apron, say again QNH, G-CD
ATC: G-CD, QNH 1015
G-ABCD: QNH 1015 G-CD

As you can see from the above example, the readback of received information is important, and ask for clarification of the missed items only.

Also is it fine to ask them to slow down if its hard to understand for example due to heavy accent?

The ICAO standard phraseology manual includes the phrase SPEAK SLOWER meaning "Reduce your rate of speech".
Source: ICAO Annex 10 - Aeronautical Telecommunications - Volume II - Communication Procedures including those with PANS status (viewable here)

Perhaps answer it more directly?

How often can it happen or how often should it happen are different questions from what you asked. You asked how often it does happen. I’d disagree from the “all the time” answer. In fact, in my experience, considering overall operations, it happens rarely. That’s not real quantifiable, so I’ll say that when I was flying a lot, there were days when I heard it maybe once or twice in a day. There were also days when I heard it more often. It just depends. However, if you’re from the South (U.S.) where we speak fairly slowly and your trip takes you up to the NYC area where they speak a bit more rapidly and with a different accent than in the South, you may find yourself needing to ask the controller to “say again” or “confirm heading two-seven-five after Alpha”, etc. There have already been some good suggestions in other answers, but the bottom line is your main job is flight safety. If you didn’t completely understand controller instructions, it’s not at all safe to continue until you do understand. Do whatever you need to do to get there (i.e., to a point of understanding).

+1 for the last sentence alone. The alternative to "Also is it fine to ask them to slow down if its hard to understand for example due to heavy accent?" is potentially killing hundreds of people!

Yes indeed. Too many worry more about how it’ll make them look than about its effect on safety.

I'm thinkin the "all the time" is ment to read as "it's not rare at all. I heard it daily, then again my airfield has a lot of training flights. There should be no stigma to transmitting say again, repeat all..., words twice or speak slower. Surely if you do that all the time at LHR or JFK you'll get the telephone number, but as you stated, safety first.

@Jpe61: Indeed.  More generally, at least in American usage, saying something happens "all the time" implies that no explanation or excuse is expected.  For a pilot to say "Acme 123, I'm afraid I didn't catch the flight level because the flight attendant dropped my coffee" would probably be a bigger annoyance than having the pilot simply transmit "Acme 123, Repeat flight level".


text:
How can I determine the level of clouds of operational significance in METAR?
Considering that
Minimum sector altitude of the airport = 10500 feet
Airport elevation from MSL = 2500 feet
What is the level of clouds of operational significance in METAR for this airport? Should we subtract the airport’s elevation from MSA?
For more explanation
If we have a broken altostratus clouds at 9000 feet height relative to the ground, which coding is correct?
1- …..7000 -RA BKN090…
2- …..7000 -RA NSC…

Codes used:

NSC: Nil significant cloud
CAVOK: Ceiling and visibility ok
BRK: Broken (5 to 7 oktas)

Abbreviations used:

WMO: World meteorological organization
METAR: Meteorological aerodrome report
AAL: Above aerodrome level
AMSL: Above mean sea level
MSA: Minimum sector altitude
CB: Cumulonimbus
TCU: Towering cumulus congestus

In your case:

Broken altostratus layer at 9,000 ft AAL.

The cloud group is usually composed of two parts, NNNhhh:

NNN: Cloud cover = BRK
hhh: Height of the base / 100, AAL = 090

So the default cloud group would be BRK090 however, from WMO in Aerodrome Reports and Forecasts - A Users’ Handbook to the Codes:

When there are no clouds below 1 500 m (5 000 ft) or below the highest minimum sector altitude, whichever is greater, no restriction to vertical visibility and the abbreviation CAVOK is not appropriate, the abbreviation NSC (Nil Significant Cloud) is used.

In your case:

Airport: 2,500 ft AMSL.
Cloud base at 9,000 AAL + 2,500 = 11,500 AMSL.
Highest MSA: 10,500 ft AMSL.

Cloud base is 1,000 ft above the MSA, use NSC in place of BRK090.
In addition if:

the horizontal visibility is 10 km or greater and
there are no CB/TCU at any altitude,

CAVOK is usable in place of visibility, present weather and cloud groups.